SUN VS. SHADE LEAF MORPHOLOGY

PLANT ECOLOGY LABORATORY

Location: The "Wild Side" of Lake Winona

Objective: To examine possible differences in the morphology of sun and shade leaves of an native annual

Hypothesis: Various morphological characteristics of leaves will differ between shaded and sunny habitats.

Agenda:

Outdoor work

1) Work in groups of 3 or 4 students to collect shade and sun leaves (20 leaves of each type) of orange jewelweed (Impatiens capensis).  Select jewelweed leaves ~10 cm from branch apices. Measure leaf thickness (nearest 0.01 mm – estimate to the best of your ability) with calipers (try to avoid leaf veins) and record values on your data sheet. Use permanent markers to number leaves (1-20) and place all sun leaves together in the same, labeled bag.  Collect 5 additional sun leaves and store them (unnumbered) in the bag with other sun leaves. Repeat collection, numbering, and storage for shade leaves (include 5 additional shade leaves).

2) Measure stem diameters (nearest 0.01 mm – estimate to the best of your ability) with a caliper at the locations where leaves were removed. Keep sun and shade plant diameters in separate categories on the data sheet.

3) Use a paper punch to remove disks (dots) from 20 leaves/leaflets in each of the two habitats: sun and shade. DO NOT USE LEAVES PREVIOUSLY COLLECTED IN #1 ABOVE.  Avoid leaf veins as much as possible. Store all shade dots in one labeled bag and sun dots in another labeled bag.

Lab work

1) Immediately upon returning to lab, weigh individual, numbered leaves to the nearest 0.01 g using the top-loading balances. Record these wet weights on the data sheet.

2) Cut out and weigh (collectvely) known (cut out) areas of the unnumbered leaves, to the nearest 0.01 g using the top-loading balances. Convert your wet leaf weights (from #1 immediately above) to leaf areas after determining a standard leaf wet weight per area (e.g., 1 g of wet leaf = ?? cm² of leaf area) for sun and shade leaves separately.. Record leaf areas on the data sheet.

3) Spread out natural leaves in labeled trays to dry, dry for 48 hours, reweigh, and record dry weights on the data sheet. Again, keep track of leaf numbers.

4) Divide your 20 shade dots into four groups of 5 dots and weigh each group of 5 collectively to the nearest 0.0001 g (0.1 mg) using the analytical balance. Record dot weights on the data sheet. Repeat for sun dots.

Analysis:

1) For your jewelweed leaves, determine mean (±SD) leaf area, leaf thickness, leaf wet weight, leaf dry weight, % water weight, disk (dot) weights (a surrogate for leaf thickness), and stem diameters for sun and shade plants.

2) Use simple t-tests to compare mean values between sun and shade leaves.

3) What variables differed between sun and shade leaves?

Equipment:

Balances, hole punches, bags, permanent markers, paper